1. Field of the Invention
The present invention relates to an apparatus for recording/reproducing information using an apparatus (Scanning Probe Microscopy; to be referred to as an SPM hereinafter) for detecting surface information in accordance with a tunneling current or force generated between a probe and a sample.
2. Related Background Art
SPMs are classified in accordance with substances to be detected. Various physical quantities such as a tunneling current, a force (e.g., an atomic force, an electrostatic force, or a magnetic force), light, and an electrostatic capacitance become detection targets. In any case, a common detection technique for detecting a physical quantity with a probe having a sharp tip is used. This detection method has recently rapidly been developed to exhibit a high spatial resolution of 0.1 nm to several tens of nm.
Along with the development of the SPM, various recording/reproduction apparatuses using the principle of SPM have been proposed. It is possible to produce a very small recording bit having a size of 1 nm to several hundreds of nm using a stimulus such as a current, an electric field, or a force generated between an SPM probe and a local area of a recording layer in accordance with a high SPM spatial resolution, thereby reproducing the recorded information. As a result, the recording density can be greatly increased.
Recording methods are classified in accordance with a change in physical shape of a surface and a change in electrical, magnetic, chemical, or optical state. Examples of the change used in the former method are physical deformation using a probe, thermal deformation using a high-energy beam such as a laser or electron beam, electric evaporation using a high electric field, and deposition of fine particles. Examples of the change used in the latter method are an electrical switching phenomenon (Japanese Laid-Open Patent Application Nos. 63-161552 and 63-161553) found in a .pi. electron-based organic compound or a chalcogen compound, charge storage (U.S. Pat. No. 4,575,822) in a silicon nitride film, various redox reactions of, e.g., a transition metal oxide, viologen, a styryl compound, rare earth diphthalocyanine, polyaniline, polythiophene, polypyrrole, and a metal-TCNQ charge-transfer complex, and a change between crystalline and noncrystalline phases using a vanadium oxide-based crystal glass.
FIGS. 1 and 2 are diagrams showing conventional recording/reproduction apparatuses, respectively. In the apparatus shown in FIG. 1 or 2, the distance between a recording layer and an SPM probe is controlled using as a servo signal a force (FIG. 1) or tunneling current (FIG. 2) generated between the probe and the recording layer, and a voltage pulse is applied between the recording layer and the probe to record or erase information.
In each conventional apparatus described above, a recording or erasing condition such as a pulse width or height in a recording or erasing voltage pulse generating circuit is fixed. No problem is posed when no defects are present in the recording layer and the thickness and quality of the recording layer are ideally uniform or homogeneous. If variations in thickness or quality of the recording area of the recording layer are present, optimal recording or erasing conditions are shifted to cause variations in produced bit sizes, failures in bit recording or erasure, and in the worst case, a decisive damage to the recording layer and the probe due to dielectric breakdown and thermal destruction.